Hello everyone,
I am trying to group/merge 3 data disks (GreenData1, 2 & 3) => refer to picture below: STEP 1, 2, 3
But this step always ends with an error. => refer to picture below: STEP 4
When this error message pops out, I press "ok" button
Press"revert" button, to cancel the changes.
Next, I proceed to "delete" the name: unionfs
But at the end, when deleting there is another delete error. => refer to picture below: STEP 5
When I click "ok" button the unionfs got deleted.
I have included the error code below.
Could anyone offer a solution to my problem?
The database of my omv gone hay-wired? 
Thank you.
Below is the error code when deleting the unsuccessful merge.........even though this error occurred, but omv was able to remove it on the list.
Error #0:
OMV\Config\DatabaseException: Failed to execute XPath query '/config/services/unionfilesystems/filesystem[uuid='4940397a-53ae-482a-9d78-025d0e3bede7']'. in /usr/share/php/openmediavault/config/database.inc:78
Stack trace:
#0 /usr/share/openmediavault/engined/rpc/unionfilesystems.inc(244): OMV\Config\Database->get('conf.service.un...', '4940397a-53ae-4...')
#1 [internal function]: OMV\Engined\Rpc\UnionFilesystems->delete(Array, Array)
#2 /usr/share/php/openmediavault/rpc/serviceabstract.inc(123): call_user_func_array(Array, Array)
#3 /usr/share/php/openmediavault/rpc/rpc.inc(86): OMV\Rpc\ServiceAbstract->callMethod('delete', Array, Array)
#4 /usr/sbin/omv-engined(537): OMV\Rpc\Rpc::call('UnionFilesystem...', 'delete', Array, Array, 1)
#5 {main}